372 



ZOOLOGY 



SECT. 



considerable resemblance to those of Mammals in the regularity of their 

 arrangement in sets, often with large canine* or tusks. Palatine teeth are 

 sometimes present. One order, the Placodontia, have remarkable broad crushing 

 teeth on both upper and lower jaws and on the palate. 



The Theromorpha only occur in beds of Permian and Triassic age, and have 

 been found in South Africa and North America, as well as Europe and India. 



Among them have recently been found 

 many transition forms which tend to 

 bridge over the interval between the 

 Reptilia and the Mammalia. 



SAUROPTERYGIA. 



The typical representatives of this 

 order, such as Plesiosaurus (Fig. 1012), 

 were aquatic Reptiles, sometimes of 

 large size (up to 40 feet), though many 



sc 



Flu. 1013. Plesiosaurus, pectoral arch. cor. 

 coracoid ; e. episteriium ; gl. glenoid cavity ; 

 ac. scapula. (After Zittel.) 



were quite small. They had a lizard- 

 like body, a very long neck, sup- 

 porting a relatively small head, and a 

 short tail which supported a vertical 

 caudal fin ; the limbs were modified to 

 form swimming-paddles. In older and 

 less specialised members of the group, 

 however, the limbs were not paddle-like, 

 but adapted for walking. 



The spinal column of the Sauro- 

 pterygia is characterised by the great 

 length of the cervical, and the shortness 

 of the caudal region. The vertebra? are 

 usually amphiccelous. The sacrum consists of either one or two vertebrae. There 

 is no sternum. In the skvdl there are large premaxillse ; a bony palate is 

 absent ; a transverse bone is present. One temporal arch only is developed. 

 There is a well-marked parietal foramen. The ring of bony plates (developed in 

 the sclerotic) found in the orbit of some fossil Reptiles is not developed. The 

 quadrate is not movable. The pectoral arch (Fig. 1013) presents some remark- 



